The density functional theory calculations were carried out by using Vienna ab initio simulation package [1]}, [2]}, [3]}. The exchange-correlation energy function was determined based on the Perdew-Burke-Ernzerhof form of the generalized gradient approximation [4]}. The structures were optimized with high accuracy. The plane-wave cutoff energy was set as 600 eV. QUANTUM ESPRESSO package [5]} was used to calculate the phonon dispersion and the electron phonon coupling (EPC) constants with the 2\(\times \) 2\(\times \) 2 q-points and 8\(\times \) 8\(\times \) 8 k-points. The Allen-Dynes-modified McMillan equation [6]} was used to calculate \(T_c\)  in the following form: \(T_c\)  = \(\frac{\omega _{log}}{1.2}\exp [-\frac{1.04(1+\lambda )}{\lambda -\mu ^\ast (1+0.62\lambda )}]\) , with \(\omega _{log}\)  = \(\exp [\frac{2}{\lambda }\int \ln (\omega )\frac{\alpha ^2F(\omega )}{\omega }d\omega ]\)  and \(\lambda \)  = 2\(\int \frac{\alpha ^2F(\omega )}{\omega }d\omega \) , where \(\mu ^\ast \) , \(\alpha ^2F(\omega )\) , and \(\lambda \)  are the Coulomb pseudopotential, the electron phonon spectral function, and the EPC parameter, respectively.
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